Module 11: Digestive PYSO PDF

Module 11: Digestive PYSO Created @November 15, 2024 9:01 AM Class PYSO001 Reviewed Types of Digestion mechanical digestion: the physical breakdown of food into smaller particles increases the s...

Module 11: Digestive PYSO Created @November 15, 2024 9:01 AM Class PYSO001 Reviewed Types of Digestion mechanical digestion: the physical breakdown of food into smaller particles increases the surface area for enzymes to come in and do their job when food is broken down Chemical Digestion: a series of hydrolysis reactions that break dietary macromolecules into their monomers (simplest components) carried out by digestive enzymes produced by the salivary glands, stomach, pancreas, and small intestine pancreas secretes the majority of the enzymes in this process Results: polysaccharides into monosaccharides Proteins into amino acids Fats into monoglycerides and fatty acids Nucleic acids into smaller nucleotides *after the enzymes are done with their reactions, we want the simplified structures from these complex structures Module 11: Digestive PYSO 1  General Anatomy Digestive Tract 30 ft long muscular tube extending from the mouth to anus GI tract is the stomach and intestines Accessory Organs consists of the teeth, tongue, salivary glands, liver, gallbladder, and pancreas Help with digestion in some aspect, mechanical or chemical Saliva starts chemical digestion in the mouth, such as starch (complex carb) and fat digestion Saliva dissolves it and break it down in order to expose to the taste buds Moistens food and binds it together and turns into a bolus Whats in saliva? mostly water It’s a solution consisting of 97% - 99.5% of water and the following enzymes: Module 11: Digestive PYSO 2  Salivary Amylase: enzyme that begins the starch digestion in the mouth (Breaks down carbohydrates) Lingual Lipase: enzyme that is activated by stomach acid and digests fat after food is swallowed( breaks down triglycerides aka lipids) - however LL is not activated in neutral pH, meaning that it is activated in by stomach acid - Mucus: helps to bind and lubricate food and turn it into a bolus Lyzozyme: enzyme that kills bacteria Immunoglobulin: fights against food borne pathogens Swallowing a reflex that is regulated by the medulla and CNX the Vagus nerve Bolus Tongue compresses food to form a bolus Bolus → Pharynx → Esophagus Upper esophageal sphincter constricts and bolus passes down Peristalsis is the segments muscle contraction that helps to push the bolus down Lower esophageal sphincter relaxes, enters the stomach Deglutition regulated by the medulla and CN10 The term for swallowing Stomach Module 11: Digestive PYSO 3  begins the chemical digestion of protein and fat Chyme is pasty mixture of semi-digested food in the stomach Primary function of the stomach is to be a food storage organ! Proteins and Fats are chemically digested in the stomach Chyme is a pasty mixture of digested food covered in stomach acid *most chemical digestion occurs after the chymes passes on to the small intestine pyloric sphincter regulates the passage of chyme into the smaller intestine the stomach is also mechanically compressing food due to the three muscle layers (longitudinal, circular, and oblique) Glands of the Stomach inside the gastric rugae, we have individual glands and pits Gastric Pits: depressions in gastric mucosa lined with simple columnar epithelium Secrete 2-3L of gastric secretions: water, HCL, Pepsin Glands open into the bottom of each gastric pit Pepsin is an enzyme released from the glands at the bottom of the gastric pits There are three variations of pits found at the bottom of the gastric pit Pyloric and Gastric Glands Module 11: Digestive PYSO 4  Gastric Glands: predominant gland in the stomach Contains G cells, chief cells, parietal cells, and mucous neck cells, Pyloric Glands: mostly found in the stomach lining of the pyloric region of the stomach contains parietal cells, mucous cells, and G cells Cells of Gastric Glands Mucous Cells secrete mucus, to help coat and liquify the bolus so the enzymes could enter and do their chemical digestions Parietal Cells found mostly in the upper half of the gland Secrete HCl, intrinsic factor and a hunger hormone called ghrelin Chief Cells only in the gastric glands Secretes gastric lipase and pepsinogen Hydrochloric Acid another word for gastric secretion is known as gastric juice Gastric juice has a high concentration of pH, 0.8 very acidic Module 11: Digestive PYSO 5  parietal cells produce HCl and contains carbonic anhydrase H+ - K+ ATPase create a channel where K is kicked into the cell (against its concentration gradient) and H out of the Cell Functions of Hydrochloric Acid 1. Causes the releases and activation of pepsin 2. Breaks up connective tissues and plant cell walls 3. Low ph destroy most bacteria/pathogens 4. Inactivate the enzyme salivary amylase (originally secreted in the mouth) briefly stopping the breakdown of carbohydrates Digestive Enzymes in Stomach Pepsinogen: a zymogen (inactive enzyme) a precursor to the actual enzyme - can recognize these by the suffix - nogen Once in the stomach, HCl helps to create Pepsin, (from pepsinogen) and function is to digest dietary proteins in the stomach into amino acids An autocatalytic effect occurs where pepsin is from and converts more zymogen (pepsinogen) into pepsin Gastric Lipase the other enzyme released by chief cells Gastric lipase play a minor role in digesting fats, 10 - 15% are digested by them and the rest is digested in the small intestine Module 11: Digestive PYSO 6  Digestion and Absorption salivary and gastric enzymes partially digest protein and some starch/fat in the mouth and stomach The stomach does not absorb any significant amount of nutrients Protection of the Stomach Stomach is protected in 3 ways from the harsh acidic environment (From its own acidic environment) 1. Mucous coat - thick, highly alkaline mucus 2. Tight junctions: between epithelial cells from the gastric juice from seeping between them 3. Epithelial cell replacement: stomach epithelial cells live only 3 to 6 days Appetite a complex study in which we are still trying to learn about Correa Lab is where Professor Misquez worked/studied Gut-Brain Peptides (Short Term) 1. Ghrelin secreted by the parietal cells in the fungus of an empty stomach Produces the sensation of hunger Module 11: Digestive PYSO 7  Once ghrelin is released, the hypothalamus releases Growth Hormone Releasing Hormone (GHRH) Signal that begins a meal 2. Peptide YY (PYY) secreted by enteroendocrine cells of ileum (last portion of the small intestines) and colon is secreted when food and chyme is in the stomach It is secreted way before the food actually gets to the stomach Purpose of the hormone is to trigger satiety or fullness 3. Cholecystokinin (CCK) secreted by the enteroendocrine cells in the duodenum and jejunum (small intestine) Stimulates the secretion of bile and pancreatic enzymes Stimulates the brain and sensory fibers of the vagus nerve in suppressing appetite Gut-Brain Peptides (Long-Term) 1. Leptin Secreted by adipocytes The signaling does get impacted when more obese people :( Module 11: Digestive PYSO 8  Leptin also regulates the female menstrual cycle Level proportionate to ones own fat stores 2. Insulin secreted by pancreatic beta cells Stimulate glucose uptake by the body’s cells Promotes glycogen and fat synthesis Weaker effect on appetite than Leptin Appetite Regulation by Hypothalamus a group of neurons in the hypothalamus that secrete a hormone called neuropeptide Y (NPY) a potent appetite stimulant Ghrelin stimulates neuropeptide Y secretion Insulin, PYY and Leptin inhibit it Accessory Digestive Organs The Liver the body’s largest gland It’s main function is to store glucose as glycolygen Secretes bile salts (aids in fat digestion) The liver is made up of hepatocytes Module 11: Digestive PYSO 9  Hepatocytes cuboidal cells surrounding central vein in liver After a meal, hepatocytes: absorb from the blood: glucose, amino acids, iron, vitamins Removes and degrades hormones, toxins, bile pigments, and drugs Secretes into the blood: albumin, lipoproteins, clotting factors, angiotensinogen In between meals, hepatocytes break down stored glycogen and releases glucose into the blood Gross Anatomy of the Gallbladder, Pancreas, and Bile Passages the liver makes bile but bile is stored in between meals in the gallbladder The Gallbladder stores the biles that was made in the liver Bile - yellow-green fluid containing minerals, cholesterol, neutral fats, phospholipids, bile pigments, and bile salts Bilirubin is the pigment color that is derived from the decomposition of hemoglobin Bile salts - synthesized from cholesterol; aid in fat (lipid) digestion/absorption Module 11: Digestive PYSO 10  Gallstone: an accumulation of hardened cholesterol Pancreas it is both a exocrine and endocrine gland Endocrine portion pancreatic islet cells (also called ilsets of langerhans) that secrete insulin and glucagon Alpha cells secrete glucagon Beta cells secrete insulin Exocrine portion 99% of the pancreas Secretes 1200 t0 1500 ml everyday of pancreatic juice every day Pancreatic Juice alkaline mixture of water, enzymes zymogens, sodium bicarbonate, and other electrolytes Bicarbonate buffer HCl arriving from the stomach There is a pH change in the duodenum Pancreatic Zymogens Zymogen - inactive form of enzyme of interest 1. Trypsinogen Module 11: Digestive PYSO 11  secreted into intestinal lumen (the inside of the duodenum) Will be converted into trypsin, which is then regulated y enterokinase (secreted by the mucosa of small intestine) Trypsin is also autocatalytic → converts more trypsinogen to trypsin 2. Chymotrypsinogen converted to chymotrypsin by trypsin 3. Procarboxpeptidase converted to carboxypeptidase by trypsin Other pancreatic enzymes pancreatic amylase - digests starch Pancreatic lipase - digests fats Ribonuclease and deoxyribonuclease: digests RNA and DNA Duodenum receiving chyme (stomach), Bile, and Pancreatic Juice Bile physically breaks down fats Pepsin is inactivated in the duodenum Pancreatic enzymes takes over the chemical digestion Module 11: Digestive PYSO 12  Jejunum especially rich blood supply, which gives it a red color Walls are relatively thick and muscular Most digestion and nutrient absorption occurs here Ileum final region of the small intestine Gross Anatomy of the Small Intestine Ileocecal junction found where the small intestine ends and the large intestine begins It is where the ileum joins the cecum of the large intestine Ilecoceal Valve a sphincter formed by the thickened muscular is of the ileum Regulates the passage of food residue into the large intestine inside the lumen of the small intestine within the villi , lacteals absorb lipids from the lumen of the small intestine Intestinal Motility Module 11: Digestive PYSO 13  segmentation: when the walls of the intestine do stationary constriction most common kind of intestinal contraction Doesn’t move food forward but mixes it in place Peristalsis: gradual movement of contents towards colon peristaltic wave begins in the duodenum Moves chyme toward colon over a period of two hours Carbohydrate Digestion Starch is the most digestible carbohydrate it is a chain of many glucose monomers Cellulose is a type of carbohydrate that can’t be digestion When starch is first broken down, its digested to oligosaccharides then into disaccharide, then finally to glucose which is absorbed by the small intestine Process begin in the mouth salivary amylase hydrolyzes starch into oligosaccharides Salivary amylase stops working in the stomach When we reach the small intestine pancreatic amylase converts starch to oligosaccharides and maltose within10 min Module 11: Digestive PYSO 14  Both these carbohydrates are in contact with the brush border enzymes (releases maltose, dextrinase, glucoamylase) and their purpose is to break down the oligosaccharides and maltose into glucose Glucose then will be small enough to be absorbed by the villi (the absorptive cells in the small intestine, the duodenum) by their capillary network Absorptive Cells they have transport proteins, and symporters, in order to help facilitate the diffusion of glucose into the cell On the basal side of the cell, there is a GLUT that kicks glucose out of the cell and into the blood capillary network Lastly there is a Na+/K+ pump that help maintain the concentration gradient Protein Digestion Proteases - enzymes that digest proteins the process of protein digestion begins in the stomach 1. Pepsin (made/ active in stomach) - hydrolyzes any peptide bond between tyrosine and phenylalanine Module 11: Digestive PYSO 15